Dentures need to be closely fitted to anatomical landmarks on the patient in order for the denture to comfortably fit as well as to be under the neuromuscular control of the patient. It is critical for the dentures to properly fit in order for the dentures to be worn comfortably and securely without the embarrassment of falling out during use.
The anatomical landmarks are typically located relative to the patient's anatomy by using a customized denture impression tray. Thermoplastic molding compound is applied along the peripheral edges of the tray which is positioned in the patient while the compound is soft. The patient manipulates their jaw while the compound is setting to provide in the impression appropriate clearances within the buccal, labial and/or lingual folds. This process is uncomfortable for the patient and does not provide precise location of the anatomical features. The resulting impressions are typically used in creating a wax rim. The wax rim is tried in the patient and marked to provide areas which need to be carved for a better fit. This requires skill on the part of the dentist and technicians.
One critical area of fit for the denture is the post dam. The post dam on a denture is a ridge along the back of the denture which presses slightly into the posterior palate to form a seal. The increased thickness of the denture along a narrow border adds pressure on the tissue and maintains a vacuum seal. Without this sealing effect, the upper denture the vacuum between the denture and the roof of the mouth is reduced or lost and the denture loosens as the wearer talks, chews or swallows. This seal is critical for the upper denture to be secure in the patient.
The ideal location for the post dam is along the junction of the hard and soft palates. The junction between the hard and soft palate where the denture border lies is neither a straight line nor of uniform consistency. It is harder in the midline and soft on both sides of the midline. Thus, an ideal post dam has to reflect the anatomy and features of that pa.tt of the mouth. If the denture extends too far to the rear of the mouth, the patient may suffer from gagging. If the denture extends too much into the hard palate, the denture will likely lose the vacuum seal and will not fit
Currently, the post dam is created on the denture by modifying the impressions or by application of a wax material to the area of the plaster model representing the roof of the mouth. Both require the use of a plaster model of the denture upon which the post dam is carved by a technician based on the estimation of where the line between the hard and soft palate occurs in the impression into the mold from the denture will be fabricated. Both techniques are less than precise in locating the ideal position. Thus the precision on where the post dam is located depends upon the quality of the impressions and the skill of the technician.
Another set of anatomical feature that are critical for the proper use of dentures are the labial and buccal frenae. The labial frenum attaches to the center of the upper lip and between the upper two front teeth while the buccal frenums attach the alveolar ridge to the cheek on each side of the mouth. If the matching notches of the denture are not located precisely for the labial frenum and the buccal frenums, the denture can often be pulled loose. Currently these frenums are visually located by the dentist or technician and the notches formed by a file in the impressions.
The rugae is typically neglected in the creation of dentures. The palatial rugae is asymmetrical and has irregular elevations of the mucosa located in the anterior third of the palate. Each individual has a unique rugae which can affect the speech of the individual. Currently, most dentures do not include a rugae and are smooth, instead. In those instances where a denture does include a rugae, the rugae is typically formed from a template rather than having a unique rugae for each patient.
Thus, presently there is no process for creating dentures that have the precise fit to or mimicking of the anatomical features of the patients mouth.